Hierarchical micro assembler system

ABSTRACT

An electrode array including a substrate. The electrode array includes a first plurality of electrodes disposed above a first zone of the substrate, wherein the first plurality of electrodes has a first range of spacing. The electrode array further includes a second plurality of electrodes disposed above a second zone of the substrate, wherein the second plurality of electrodes has a second range of spacing that is less than the first range of spacing.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

This invention was made with Government support under contractFA8650-15-C-7544 awarded by the Defense Advanced Research ProjectsAgency. The Government has certain rights in this invention.

BACKGROUND

Xerographic micro assembly is a method of fabricating devices usingxerographic like, electrostatic force based directed assembly techniquesto assemble functional micro objects to complex device structure. Mobilemicro objects may be immersed in an assembly medium that covers anelectrode array. An electric field pattern may be applied to theelectrode array that attracts the mobile micro objects. The electricfield pattern may attract or repel the mobile micro objects, which mayguide the mobile micro objects into a specific position and orientationabove the electrode array.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure described herein is illustrated by way of exampleand not by way of limitation in the accompanying figures. For simplicityand clarity of illustration, features illustrated in the figures are notnecessarily drawn to scale. For example, the dimensions of some featuresmay be exaggerated relative to other features for clarity. Further,where considered appropriate, reference labels have been repeated amongthe figures to indicate corresponding or analogous elements.

FIG. 1 illustrates a micro assembly system in accordance withembodiments of the present disclosure.

FIG. 2 illustrates an electrode array having a first zone and a secondzone, according to implementations.

FIG. 3 illustrates an electrode array having electrodes with adecreasing range of spacing, according to implementations.

FIG. 4 illustrates a multi-phase electrode assembly, according toimplementations.

FIG. 5 is an illustration of an electrode array having a first zone tostore mobile micro objects, according to implementations.

FIG. 6 illustrates an electrode array having a first zone to storeintermediate assemblies of mobile micro objects.

FIG. 7 illustrates an electrode array unit having light sourcesilluminating the first zone and second zone.

FIG. 8 illustrates an electrode array unit having a transfer film,according to implementations.

FIG. 9 illustrates a process flow for fabricating an electrode array,according to implementations.

DETAILED DESCRIPTION

In the following description, various aspects of the illustrativeimplementations will be described using terms commonly employed by thoseskilled in the art to convey the substance of their work to othersskilled in the art. However, it will be apparent to those skilled in theart that the present disclosure may be practiced with only some of thedescribed aspects. For purposes of explanation, specific numbers,materials and configurations are set forth in order to provide athorough understanding of the illustrative implementations. However, itwill be apparent to one skilled in the art that the present disclosuremay be practiced without the specific details. In other instances,well-known features are omitted or simplified in order not to obscurethe illustrative implementations.

Demand for semiconductor devices having high densities of surfacemounted components continues to increase. For example, a semiconductordevice may contain hundreds or thousands of surface mounted componentsthat must be placed on a substrate in the proper position with thecorrect orientation. One method of placing these surface mountedcomponents is known as micro assembly. In micro assembly, a plurality ofmobile micro objects (e.g., chiplets) may be immersed in an assemblymedium (e.g., a dielectric fluid). An electrode array may be submergedin a container having the assembly medium containing the mobile microobjects. The electrode array may generate a patterned field to positionand orient the mobile micro objects in locations above the electrodearray by selectively energizing individual electrodes of the electrodearray. The field generated by the electrode array may exertelectrophoretic or dielectrophoretic forces on the mobile micro objectscausing the mobile micro objects to move relative to the assembly mediumand the array. The position may refer to a point or place relative tothe electrode array. The orientation may be the rotation of the mobileparticle relative to the electrode array. The mobile micro objects maybe moved, via the field, above the surface of the electrode array untileach of the mobile micro objects is positioned and oriented at alocation above the electrode array. Once the mobile micro objects are inthe specific locations, the electrode array may be used to transport themobile micro objects, where they may be transferred to a finalsubstrate. Challenges of micro assembly may include large amounts ofcomputing data being required to selectively energize and monitor theindividual electrodes of the electrode array. If the density ofelectrodes on the electrode array remains constant, as the size of theelectrode array increases the amount of computing data requiredincreases proportionately to the area of the electrode array. Increasingthe refresh rate (e.g., how frequently computations are performed)further increases the amount of computing data required. Furthermore,manufacturing an electrode array having a high density of electrodesrequires the use of more expensive manufacturing processes, makingproducing electrode arrays on larger scales impractical. Moreover, dueto scaling of the field generated by the electrodes, only a low voltage(e.g., less than 10 volts) may be provided to electrode arrays having ahigh density of electrodes before failure may occur, despite highvoltages (e.g. >100V) being desirable in particular situations.

The present disclosure addresses the above-mentioned and otherdeficiencies by providing for an electrode array having a first zone(e.g., low resolution zone) having electrodes spaced relatively farapart that may coarsely position and orient the mobile micro objectswithin a defined area. The electrode array may have a second zone (e.g.,high resolution zone) having electrodes spaced closer together than thefirst zone that may more precisely position and orient the mobile microobjects at specific locations and orientations within the defined area.The present disclosure may reduce the amount of computational datarequired to selectively energize and monitor the individual electrodesof the electrode array by decreasing the total number of electrodes. Thepresent disclosure may decrease manufacturing costs of the electrodearray by allowing portions of the electrode array (e.g. the lowresolution zone) to be manufactured using less expensive methods. Thepresent disclosure may allow higher voltages to be used in lowresolution zones than in higher resolution zones without failureoccurring. In implementations, the electrode assembly includes asubstrate having a first zone including a first plurality of electrodesand a second zone including a second plurality of electrodes thatconduct a field to control the movement of the mobile particle topredefined positions and orientations respective to the electrode array.

FIG. 1 is a cross-sectional view of a micro assembly unit 100 for usewith implementations of the present disclosure. The micro assembly unit100 includes a container that holds an assembly medium 120. In someimplementations, the assembly medium 120 may be a dielectric fluid. Inother implementations, the assembly medium 120 may be a gas, such asnitrogen. The mobile micro objects 110 may be immersed in the assemblymedium 120 as illustrated in FIG. 1. In one implementation, the mobileparticle 110 may be any particle that has at least one substantiallyplanar surface. The substantially planar surface may be a surface of themobile particle having a local roughness (e.g., height of a feature onthe substantially planar surface) that is less than 10% of the length ofthe particle. In other implementations, the mobile particle 110 may bespherical, ellipsoidal or any other suitable geometry. In someimplementations, the mobile particle 110 may have an electrical chargeor magnetic moment that allows the mobile particle 110 to be attractedor repelled by a field (e.g., electric field or magnetic field) createdby an electrode array 130. In another implementation, the mobileparticle 110 may not have an electrical charge and may be moved abovethe surface of the electrode array 130 using induced dipole forces. Inone implementation, the electrode array 130 may include a substratehaving non-planar structures. In another implementation, the electrodearray 130 may include a substrate having a substantially planar surface.The electrode array 130 may be submerged into or coated by the assemblymedium 120.

In one implementation, the substrate may have embedded electroniccomponents. In another implementation, the substrate may haveelectronics placed on a surface opposite the electrodes and connected tothe electrodes through vias. In yet another implementation, thesubstrate may be a non-planar substrate where the electrodes may bedisposed above non-planar features of the substrate. In a furtherimplementation, a planar substrate may be etched to form non-planarfeatures on a surface of the substrate.

In one implementation, the electrode array 130 may be coupled to acontroller 140. The controller 140 may determine which individualelectrodes of the electrode array 130 are energized in order to generatea desired field to attract, position and orient of the mobile microobjects 110 at a position above the electrode array 130. The controller140 may be coupled to a power source 150. The power source 150 mayprovide power or field to the electrode array 130 using the controller140 in order to generate the field. In one implementation, the generatedfield may be an electric field produced by stationary or oscillatingcharges of the electrode array 130. In another implementation, thegenerated field may be a magnetic field produced by moving charges(i.e., current) of the electrode array 130. In a further implementation,the generated field may be an electromagnetic field that includes boththe electric field and magnetic field components of the electrode array130.

In another implementation, the electrode array 130 may be coupleddirectly to power source 150. The electrode array 130 may include aplurality of phototransistors, which may become energized in response toexposure to light. A surface of the electrode array 130 may be exposedto light from an optical projector 160 (also referred to as “lightsource” hereafter), where the optical projector projects an imagecorresponding to the specific position and orientation of the mobilemicro objects 110. The phototransistors illuminated by the image maygenerate a field to attract, position and orient the mobile microobjects 110 to a location above the electrode array 130. Thephototransistors that are not illuminated by the projected image may notchange or generate a field. For illustration purposes, light source 160is shown above the electrode array 130 and projecting an image onto thetop surface of the electrode array 130. However, in anotherimplementation, the light source 160 may be located below the electrodearray 130 and project the image onto the bottom surface of the electrodearray 130.

FIG. 2 illustrates an electrode array 200 having a first zone and asecond zone, according to implementations. The electrode array 200 maybe representative of electrode array 130 of FIG. 1. The electrode array200 may include electrodes 220 disposed on the surface of substrate 210.The electrodes 220 may be any conductive material. Examples ofconductive material include, but are not limited to, copper, gold,silver, indium tin oxide (ITO) film or composite materials. In oneimplementation, the electrodes 220 may be disposed on the surface of thesubstrate 210 using a photolithography process that uses light totransfer a pattern to the substrate. The photolithography process mayinclude an etching process to remove one or more layers (or parts of oneor more layers) from the surface of the substrate 210. The etchingprocess may include dry etch or wet etch. In another implementation, theelectrodes 220 may be disposed on the surface of the substrate 210 usinga soft lithography process that uses patterned elastomeric stamps. Inyet another implementation, the electrodes 220 may be disposed on thesurface of the substrate 210 using high resolution patterning (e.g.,multiple patterning), where the substrate 210 is exposed to multiplelithographic processes. In one implementation, a dielectric layer (notshown) may be disposed above the surface of the substrate 210 andelectrodes 220.

The electrode array 200 may include a first zone 230 (e.g., lowresolution zone) and a second zone 240 (e.g., high resolution zone). Thefirst zone 230 may include electrodes 220 having a first range ofspacing 250. The first range of spacing 250 may be the distance from thecenter of one electrode in the first zone 230 to the center of anadjacent electrode. In one implementation, the first range of spacingmay be between 15-1000 microns, inclusively. The second zone 240 mayinclude electrodes 220 having a second range of spacing 260. The secondrange of spacing 260 may be the distance from the center of oneelectrode in the second zone 240 to the center of an adjacent electrode.In one implementation, the second range of spacing 260 may be between1-50 microns, inclusively. In another implementation, the second rangeof spacing 260 may be less than the first range of spacing 250. Forillustration purposes, the first zone 230 and the second zone 240 areshown as covering a similar area of the surface of the substrate 210.However, in another implementation, the first zone 230 may cover alarger area than the second zone 240 or vice versa. In a furtherimplementation, the electrode array 200 may include multiple first zones230 and/or second zones 240 having varying geometries. In yet anotherimplementation, the geometries and locations of the first zones 230and/or second zones 240 may be based on a micro assembly process, wherethe geometries and locations of the first zones 230 and/or second zones240 may be determined in order to optimize the micro assembly process.The micro assembly process may be optimized by minimizing the distancethe mobile micro objects are required to travel above the surface of theelectrode array 200 and/or minimizing the time required to position themobile micro objects in their specific position and orientation.

FIG. 3 illustrates an electrode array 300 having electrodes with adecreasing range of spacing, according to implementations. The electrodearray 300 may be representative of electrode array 130 of FIG. 1. Theelectrode array 300 may include electrodes 320 disposed on the surfaceof substrate 310. The electrodes may be disposed on the surface of thesubstrate 310 using a photolithography process, a soft lithographyprocess, high resolution patterning or any similar process. Theelectrodes 310 may have a first range of spacing 320 and a second rangeof spacing 330. The first range of spacing 320 may be the distance fromthe center of one electrode to the center of an adjacent electrode. Inone implementation, the first range of spacing 320 may be between15-1000 microns, inclusively. Moving from the left side to the rightside of the electrode array 300, the range of spacing may incrementallydecrease or increase (e.g., a gradient in spacing). The electrodes 310near the right side of the electrode array 300 may have a second rangeof spacing 330. In one implementation, the second range of spacing 330may be between 1-50 microns, inclusively. In another implementation, thesecond range of spacing 330 may be less than the first range of spacing320. In one implementation, the first zone 230 and/or second zone 240may have electrodes with a decreasing range of spacing. In anotherimplementation, the range of spacing of the electrodes in the first zone230 may decrease near the second zone 240. In a further implementation,the range of spacing of the electrodes of the second zone 240 maydecrease near the center of the second zone 240. In a furtherimplementation, the range of spacing of the electrodes 310 may bedependent on a micro assembly process, where the range of spacing of theelectrodes 310 may be determined in order to optimize the micro assemblyprocess as previously discussed. For illustration purposes, electrodearray 300 is shown having a linear gradient in the spacing ofelectrodes, where the range of spacing decreases from the left side ofthe electrode array 300 to the right side of the electrode array 300.However, in some implementations, the electrode array 300 may have aradial gradient in the spacing of electrodes, where the range of spacingdecreases from the outside of the electrode array 300 to the center ofthe electrode array 300.

FIG. 4 illustrates a multi-phase electrode assembly 400, according toimplementations. The multi-phase electrode assembly 400 may be disposedon the surface of a substrate, such as substrates 210 and 310 of FIGS. 2and 3, respectively. The multi-phase electrode assembly 400 may includetraces 405, 410, 415 and 420. Traces 405, 410, 415 and 420 may be anyconductive material. Examples of conductive material include, but arenot limited to, copper, gold, silver, or composite materials. Traces405, 410, 415 and 420 may be disposed using a photolithography process,a soft lithography process, high resolution patterning or any similarprocess. The multi-phase electrode assembly 400 may also includeelectrodes 425, 430, 435 and 440. Electrodes 425, 430, 435 and 440 maybe any conductive material. Examples of conductive material include, butare not limited to, copper, gold, silver, ITO film or compositematerials. Electrodes 425, 430, 435 and 440 may be disposed using aphotolithography process, a soft lithography process, high resolutionpatterning or any similar process. In some implementations, a dielectriclayer (not shown) may be disposed above traces 405, 410, 415 and 420 andbelow electrodes 425, 430, 435 and 440, forming an electricallyinsulating layer between traces 405, 410, 415 and 420 and electrodes425, 430, 435 and 440. The multi-phase electrode assembly 400 mayinclude vias 445 through the dielectric layer to couple electrodes 425,430, 435 and 440 to traces 405, 410, 415 and 420, respectively. In someimplementations, a dielectric layer (not shown) may be disposed aboveelectrodes 425, 430, 435 and 440.

Traces 405, 410, 415 and 420 may receive power from a power source, suchas power source 150 of FIG. 1. The voltage supplied to traces 405, 410,415 and 420 may then be sequentially changed using a controller, such ascontroller 140 of FIG. 1. For example, initially traces 405, 410, 415and 420 may all receive power at the same voltage from the power source150. Then, the controller 140 may decrease or increase the voltage oftrace 405. Following this, the voltage of trace 405 may be returned toits original value and the controller may decrease or increase thevoltage of trace 410. This process may be repeated sequentially fortraces 415 and 420. By sequentially changing the voltage on traces 405,410, 415 and 420 electrodes 425, 430, 435 and 440 may generate apotential wave (e.g., electric wave or magnetic wave) to move the mobilemicro objects above the surface of an electrode array. As the voltage oftraces 405, 410, 415 and 420 are sequentially changed, a mobile particlemay move (e.g., surf) the potential wave down the multi-phase electrodeassembly 400, as illustrated by arrow 450. As the mobile particle movesdown the multi-phase electrode assembly 400, the potential wave may alsomove the mobile particle towards the center of the multi-phase electrodeassembly, as illustrated by arrows 455. Although the multi-phaseelectrode assembly 400 may be illustrated as a four phase electrodeassembly, in other embodiments the multi-phase electrode assembly 400may include more or less phases.

FIG. 5 is an illustration of an electrode array 500 having a first zoneto store mobile micro objects, according to implementations. Theelectrode array 500 may include a first zone 230 (e.g., low resolutionzone) and a second zone 240 (e.g., high resolution zone). Forillustration purposes, the electrodes of the first zone 230 and secondzone 240 are not shown. Mobile micro objects 510, 520 and 530 may belocated above the electrode array 500 and at least partially submersedin an assembly medium. In implementations, the mobile micro objects 510,520 and 530 may correspond to three different types of mobile microobjects. In one implementation, the mobile micro objects 510, 520 and530 may be disposed in separate areas of the first zone 230 where theyare stored separately from one another. The mobile micro objects 510,520 and 530 may be held in place by a field generated by the electrodesof the electrode array 500 until they are needed for a micro assemblyprocess. In another implementation, the mobile micro objects 510, 520and 530 may have associated charges and may be disposed in the same areaof the first zone 230. The field generated by the electrodes of thefirst zone 230 may arrange the mobile micro objects 510, 520 and 530into separate areas of the first zone 230 based on the associatedcharges.

During the micro assembly process when one or more of the mobile microobjects 510, 520 and 530 are needed, the field generated by theelectrodes of the first zone 230 may move the one or more mobile microobjects 510, 520 and 530 along the surface of the electrode array 500from the first zone 230 to the second zone 240 as illustrated by thearrows of FIG. 5. When the one or more mobile micro objects 510, 520 and530 arrive in the second zone 240 (e.g., high resolution zone) the oneor more mobile micro objects 510, 520 and 530 may be moved into aspecific position and orientation by the field generated by theelectrodes in the second zone 240.

FIG. 6 illustrates an electrode array 600 having a first zone to storeintermediate assemblies of mobile micro objects. The electrode array 600may include a first zone 230 (e.g., low resolution zone) and a secondzone 240 (e.g., high resolution zone). For illustration purposes, theelectrodes of the first zone 230 and second zone 240 are not shown.Mobile micro objects 510, 520 and 530 may be located above the electrodearray 600 and at least partially submersed in an assembly medium. Inimplementations, the mobile micro objects 510, 520 and 530 maycorrespond to three different types of mobile micro objects. In oneimplementation, a field may be generated by the electrodes of the firstzone 230 of the electrode array 600 to coarsely position and orientmobile micro objects 510, 520 and 530 within a defined area to form acoarse intermediate assembly, as will be discussed in FIG. 8. The mobilemicro objects 510, 520 and 530 may be moved from the first zone 230 tothe second zone 240 and into a specific position and orientation aspreviously described in FIG. 5 to create an intermediate assembly 610.The intermediate assembly 610 may include two or more of mobile microobjects 510, 520 and 530 arranged in specific positions andorientations. Once the intermediate assembly 610 has been assembled, thefield generated by the electrodes in the second zone 240 may move theintermediate assembly 610 above the surface of the electrode array 600into the first zone 230. The electrodes of the first zone 230 may thenmove the intermediate assembly 610 to a desired area for storage. Insome implementations, this process may be repeated to create multipleintermediate assemblies 610 to be stored in the first zone 230. In otherimplementations, various intermediate assemblies may be created fromdifferent combinations and arrangements of mobile micro objects 510, 520and 530 to be stored above the first zone 230.

FIG. 7 illustrates a micro assembler unit 700 having light sourcesilluminating the first zone and second zone. The micro assembler unit700 may include light sources 710 and 720. Light sources 710 and 720 maybe similar to light source 160 of FIG. 1. The micro assembler unit 700may include an electrode array 730 having a first zone 230 (e.g., lowresolution zone) and a second zone 240 (e.g., high resolution zone). Thefirst zone 230 and second zone 240 may include a plurality ofphototransistors, which may become energized in response to exposure tolight. The surface of the first zone 230 of the electrode array 730 maybe exposed to light from light source 710, where the light source 710projects an image corresponding to a field to position and orient themobile micro objects. The phototransistors illuminated by the image maygenerate a field to attract, position and orient the mobile microobjects to a location above the electrode array 730. Thephototransistors that are not illuminated by the projected image may notgenerate a field. Similarly, the surface of the second zone 240 of theelectrode array 730 may be exposed to light from light source 720, wherethe light source 720 projects an image corresponding to a field toposition and orient the mobile micro objects. For illustration purposes,light sources 710 and 720 are shown above the electrode array 730 andprojecting images onto the top surface of the electrode array 730.However, in another implementation, light sources 710 and 720 may belocated below the electrode array 730 and project the image onto thebottom surface of the electrode array 730.

In one implementation, the first zone 230 and the second zone 240 mayinclude phototransistors and electrodes having the same range ofspacing. The field generated by the electrode array 730 in the firstzone 230 and the second zone 240 may be dependent on the resolution ofthe images projected on the surface of the electrode array 730 fromlight sources 710 and 720. In another implementation, one or both oflight sources 710 and 720 may include a zoom lens (not shown) to changethe focal length of one or both of light sources 710 and 720. The zoomlens may change the resolution of the image projected on the surface ofthe electrode array 730 by of one or both of light sources 710 and 720.In a further implementation, light sources 710 and 720 may be positionedat different distances from the electrode array 730 to change theresolution of the image projected on the surface of the electrode array730.

FIG. 8 illustrates a micro assembler unit 800 having a transfer film,according to implementations. The micro assembler unit 800 may include atransfer film 810 that is located between electrode array 820 and mobilemicro objects 510, 520 and 530, as illustrated in cross-sectional viewA-A. The transfer film 810 may be formed of dielectric material,plastic, glass or any suitable material. The transfer film 810 may belocated above the first zone 230 of the electrode array 820. A fieldpattern may be generated by the electrodes (not shown) of the first zone230 of the electrode array 820 to coarsely position and orient mobilemicro objects 510, 520 and 530 within a defined area to form a coarseintermediate assembly 830. In implementations, one coarse intermediateassembly 830 may have mobile micro objects 510, 520 and 530 in adifferent position and orientation within the defined area when comparedto a second coarse intermediate assembly 830. In one implementation,once mobile micro objects 510, 520 and 530 have been coarsely positionedabove the first zone 230, the transfer film 810 may be relativelyrepositioned (e.g., by translating either the transfer film 810 or themicroassembler 820) above the second zone 240 of the electrode array820, as illustrated by the arrows of FIG. 8. After the transfer film 810has been positioned above the second zone 240, the electrodes (notshown) of the second zone 240 may generate a field to finely positionand orient mobile micro objects 510, 520 and 530 into a specificposition and orientation within a defined area to form an intermediateassembly 840. In implementations, one intermediate assembly 840 may havemobile micro objects 510, 520 and 530 in approximately the same positionand orientation as a second intermediate assembly 840. In oneimplementation, the mobile micro objects 510, 520 and 530 may bepositioned and oriented in intermediate assemblies 840 and may have atolerance between +/−1 micron and +/−10 microns, inclusive. In anotherimplementation, once mobile micro objects 510, 520 and 530 have beencoarsely positioned above the first zone 230, the electrode array 820may be repositioned so that the second zone 240 of the electrode array820 is below mobile micro objects 510, 520 and 530. After the secondzone 240 of the electrode array 820 has been positioned below mobilemicro objects 510, 520 and 530, the electrodes of the second zone 240may generate a field to finely position and orient the mobile microobjects 510, 520 and 530 into a specific position and orientation toform the intermediate assembly 840.

FIG. 9 illustrates a process flow 900 for fabricating an electrodearray, according to implementations. At block 910, a substrate may beprovided. In one implementation, the substrate may be a substantiallyplanar substrate. In another implementation, the substrate may includenon-planar structures. At block 920, electrodes may be disposed above afirst zone of the substrate. The electrodes may be disposed using aphotolithography process, a soft lithography process, high resolutionpatterning or any similar process. In one implementation, the electrodesdisposed above the first zone may have a range of spacing between15-1000 microns, inclusively. In another implementation, the electrodesdisposed above the first zone may have a range of spacing that decreasesnear the second zone of the substrate. In a further implementation, theelectrodes disposed above the first zone may have a range of spacingthat is determined in order to optimize a micro assembly process.

At block 930, electrodes may be disposed above a second zone of thesubstrate. The electrodes may be disposed using a photolithographyprocess, a soft lithography process, high resolution patterning or anysimilar process. In one implementation, the electrodes disposed abovethe second zone may have a range of spacing between 1-50 microns,inclusively. In another implementation, the range of spacing of theelectrodes disposed above the second zone may be less than the range ofspacing of the electrodes disposed above the first zone. In anotherimplementation, the electrodes disposed above the second zone may have arange of spacing that decreases near the center of the second zone. In afurther implementation, the electrodes disposed above the second zonemay have a range of spacing that is determined in order to optimize amicro assembly process.

Various operations are described as multiple discrete operations, inturn, in a manner that is most helpful in understanding the presentdisclosure, however, the order of description may not be construed toimply that these operations are necessarily order dependent. Inparticular, these operations need not be performed in the order ofpresentation.

The terms “over,” “above” “under,” “between,” and “on” as used hereinrefer to a relative position of one material layer or component withrespect to other layers or components. For example, one layer disposedabove or over or under another layer may be directly in contact with theother layer or may have one or more intervening layers. Moreover, onelayer disposed between two layers may be directly in contact with thetwo layers or may have one or more intervening layers. In contrast, afirst layer “on” a second layer is in direct contact with that secondlayer. Similarly, unless explicitly stated otherwise, one featuredisposed between two features may be in direct contact with the adjacentfeatures or may have one or more intervening layers. The words “example”or “exemplary” are used herein to mean serving as an example, instance,or illustration. Any aspect or design described herein as “example’ or“exemplary” is not necessarily to be construed as preferred oradvantageous over other aspects or designs. Rather, use of the words“example” or “exemplary” is intended to present concepts in a concretefashion. As used in this application, the term “or” is intended to meanan inclusive “or” rather than an exclusive “or.” That is, unlessspecified otherwise, or clear from context, “X includes A or B” isintended to mean any of the natural inclusive permutations. That is, ifX includes A; X includes B; or X includes both A and B, then “X includesA or B” is satisfied under any of the foregoing instances. In addition,the articles “a” and “an” as used in this application and the appendedclaims may generally be construed to mean “one or more” unless specifiedotherwise or clear from context to be directed to a singular form.Moreover, use of the term “an implementation” or “one implementation”throughout is not intended to mean the same implementation orimplementation unless described as such. The terms “first,” “second,”“third,” “fourth,” etc. as used herein are meant as labels todistinguish among different elements and may not necessarily have anordinal meaning according to their numerical designation.

It will be appreciated that variants of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be combined intomany other different systems of applications. Various presentlyunforeseen or unanticipated alternatives, modifications, variations, orimprovements therein may be subsequently made by those skilled in theart which are also intended to be encompassed by the following claims.

What is claimed is:
 1. An electrode array comprising: a substrate; afirst plurality of electrodes disposed above a first zone of thesubstrate, wherein the first plurality of electrodes has a first rangeof spacing; and a second plurality of electrodes disposed above a secondzone of the substrate, wherein the second plurality of electrodes has asecond range of spacing that is less than the first range of spacing. 2.The electrode array of claim 1, further comprising: a dielectric layerdisposed above the first plurality of electrodes and the secondplurality of electrodes.
 3. The electrode array of claim 1, wherein thefirst range of spacing of the first plurality of electrodes is between15-1000 microns, inclusive.
 4. The electrode array of claim 1, whereinthe second range of spacing of the second plurality of electrodes isbetween 1-50 microns, inclusive.
 5. The electrode array of claim 1,further comprising a transfer film disposed above the first plurality ofelectrodes and the second plurality of electrodes, wherein the transferfilm is translatable relative to the first plurality of electrodes andthe second plurality of electrodes.
 6. The electrode array of claim 1,wherein the first range of spacing corresponds to different sizes inspacing between pairs of electrodes of the first plurality of electrodesand the second range of spacing corresponds to different sizes inspacing between pairs of electrodes of the second plurality ofelectrodes.
 7. The electrode array of claim 6, wherein the first rangeof spacing corresponds to a first spacing between a first electrode anda second electrode of the first plurality of electrodes, and a secondspacing between the second electrode and a third electrode of theplurality of electrodes, wherein the second spacing is less than thefirst spacing and closer to the second zone of the substrate.
 8. Theelectrode array of claim 6, wherein the second range of spacingcorresponds to a first spacing between a first electrode and a secondelectrode of the second plurality of electrodes, and a second spacingbetween the second electrode and a third electrode of the plurality ofelectrodes, wherein the second spacing is less than the first spacingand closer to the center of the second zone of the substrate.
 9. Theelectrode array of claim 1, wherein at least one of a location or ageometry of at least one of the first zone of the substrate or thesecond zone of the substrate are determined to optimize a micro assemblyprocess.
 10. The electrode array of claim 1, wherein the first range ofspacing of the first plurality of electrodes and the second range ofspacing of the second plurality of electrodes comprise a gradient inspacing.
 11. A system comprising: an assembly medium; a plurality ofmobile micro objects at least partially submersed in the assemblymedium; and an array, at least partially disposed in the assemblymedium, the array comprising: a substrate; a first plurality ofelectrodes disposed above a first zone of the substrate, wherein thefirst plurality of electrodes has a first range of spacing; and a secondplurality of electrodes disposed above a second zone of the substrate,wherein the second plurality of electrodes has a second range of spacingthat is less than the first range of spacing.
 12. The system of claim11, further comprising: a dielectric layer disposed above the firstplurality of electrodes and the second plurality of electrodes.
 13. Thesystem of claim 11, further comprising: a transfer film disposed abovethe first plurality of electrodes and the second plurality ofelectrodes.
 14. The system of claim 11, further comprising: a powersource operatively coupled to the array to provide power to the firstplurality of electrodes and the second plurality of electrodes and toprovide a field to facilitate the movement of each of the plurality ofmobile micro objects through the assembly medium to a predeterminedposition and orientation.
 15. The system of claim 11, furthercomprising: a controller operatively coupled to the power source tocontrol a field conducted through individual electrodes of the firstplurality of electrodes and the second plurality of electrodes.
 16. Thesystem of claim 11, wherein the first plurality of electrodes and thesecond plurality of electrodes are comprised of phototransistors togenerate a field in response to illumination by a light source.
 17. Thesystem of claim 11, further comprising: a light source to illuminateindividual electrodes of at least one of the first plurality ofelectrodes or the second plurality of electrodes to control a field tofacilitate the movement of each of the plurality of mobile micro objectsthrough the assembly medium to a predetermined position and orientation.18. The system of claim 17, wherein the light source to illuminate theindividual electrodes of the first plurality of electrodes, the systemfurther comprising: a second light source to illuminate individualelectrodes of the second plurality of electrodes to control a field tofacilitate the movement of each of the plurality of mobile micro objectsthrough the assembly medium to the predetermined position andorientation.
 19. The system of claim 11, wherein the first zone is tostore the plurality of mobile micro objects at least partially submersedin the assembly medium.
 20. The system of claim 11, wherein the firstzone is to store an intermediate assembly of the plurality of mobilemicro objects.